This invention relates to the automatic testing of bare printed circuit boards, and more particularly, to an automatic loading and locating mechanism for a fault verification and repair station.
Traditional manual bare circuit board fault verification has been a tedious process. Most of the associated equipment merely provided a visual aid in the fault verification process. Typically a flying prober would be utilized for this purpose which traditionally was used to test prototype circuit boards providing the benefit that a test fixture did not have to be devised for the prototype circuit board. Using a flying prober provided the benefit of making it easier to test fine pitch test sites on the circuit boards. A problem with flying probers is that they are slow in testing the circuit board due to the requirement for manually contacting each required test site on the circuit board, which in contrast to a fixture which can test all the test sites on the circuit board simultaneously.
Traditional repair stations have also been used for fault verification for bare circuit boards. Traditional repair stations are graphics based having software which illustrates the circuitry to indicate where the possible failure could be. The repair station utilizes the failure data from the tester and verifies the failure data by hand placement of probers. Software used in connection with traditional repair stations provides risk areas for areas such as shorts or opens based upon the physical layout of the circuitry and the likelihood of leads in close proximity to each other. Conventional repair stations simply helped an operator locate a failed net end point designated by the tester, but stopped short of helping verify the fault and tracking down the location of the actual defect.
Flying probers have also been used as repair stations to verify error data from a tester. Typically there are two kinds of flying probers, namely, vertical probers and horizontal probers. In a vertical flying prober, the circuit board to be tested stands vertically upright and a probe contacts the board from either side depending upon the test site locations. The board is manually loaded and held in an upright position by hand manipulated clamps which are moved to the appropriate position and tightened to secure the circuit board. A disadvantage with vertical flying probers is that it is time consuming to manually move each clamp into position and manually manipulate the clamp to secure the circuit board. In the horizontal flying prober, the circuit boards are manually loaded into a drawer which is pulled out from the frame structure of the prober. Clamps hold the board to secure the circuit boards in a horizontal position. Again, the disadvantage in a horizontal flying prober is the time consuming and labor intensive procedure of manually loading boards in the drawer for testing. Consequently,
Consequently, a need exists for a flying prober verification and repair station with an improved loading and locating mechanism which quickly and accurately loads the printed circuit boards into the prober for testing.
The present invention is a automated bare board fault verification and repair station having a locating and loading mechanism which automatically secures the circuit board to be tested or unit under test (UUT) in position. The fault verification and repair station of the present invention will also be referred to as a flying prober. The flying prober of the present invention includes, preferably, two X-Y-Z prober heads positioned on one side of the unit under test which move independently across the surface of the circuit board to contact the desired test locations on the circuit board. Although two prober heads are preferred, more or less can be used, and on one or both sides of the UUT. The flying prober further includes electronic hardware and software for measuring isolations and continuities of the test sites electrically connected to the prober heads. The prober further includes a loading and locating mechanism for automatically securing the unit under test on the prober relative to the prober heads.
The loading and locating mechanism includes an upper housing and a lower housing one each positionable at opposite ends of the circuit boards. The housings include a lower lip for resting the edges of the circuit board on the housing. The lower housing is fixed on the frame of the flying prober and the upper housing is adjustable by screw clamps to accommodate different sized circuit boards. Positioned inside each of the upper housing and the lower housing is a movable clamping block having a plurality of finger springs rotatable by a dowel rod to lift and lower the springs above the upper surface of the circuit board. An air cylinder on either end of the clamping blocks moves the clamping block forward and backward. Similarly, an air cylinder, or other suitable actuator rotates the dowel rod to raise and lower the finger springs.
In operation, the upper housing is manually set to the desired positioned according to the specific size of the circuit board to be tested by securing the screw clamps to the frame. The circuit board to be tested is then positioned on the housing such that the edges of the circuit board rest on the lip of the upper and lower housing. Because the frame is angled, gravity allows the circuit board to be located on the clamping mechanism. With the finger springs in a raised position, the clamping blocks are actuated forward towards the circuit board to position the ends of the finger springs over the edge of the circuit board. The dowel rod is then actuated to lower the finger springs into contact with the upper surface of the circuit board along the edge to securely clamp the circuit board in the flying prober. The prober heads are then actuated across the surface of the circuit board to conduct the fault verification process. The dowel rod, clamping block and prober heads are automatically operated and controlled by the software programed within the flying prober.